The invention lies in the field of methods for making metal alloys used in making steel and other ferrous alloys.
The advantages of alloying rare earth metals and other metals with steel and other ferrous alloys to impart desirable properties thereto are well known. Typical steel-making processes utilizing rare earth metals, for example, are illustrated by those disclosed in U.S. Pat. Nos. 2,683,661, 2,683,662 and 2,683,663. Representative alloys are disclosed in U.S. Pat. Nos. 3,250,609 and 3,295,963.
It has been the practice in making the rare earth metal alloys to use metal-silicon alloys as the reducing agents, typically, calcium silicide. Representative methods are discussed in U.S. Pat. Nos. 3,250,609, 3,256,087, 3,295,963 and 3,537,884.
In the prior art methods utilizing calcium-silicon alloys for making rare earth metal alloys as illustrated by some of the cited patents, the method is ordinarily begun by making a melt of calcium silicide, followed by addition of rare earth metal oxides to make the final alloy. Also, CaSi can be mixed with the oxides and the mixture heated to molten state to form the rare earth silicide. Although the use of calcium-silicon alloys as reducing agents in the manufacture of rare earth metal alloys has been successful, the procedure is subject to improvement. First of all, the high cost of the commercial calcium-silicon alloy is a disadvantage. Further, calcium-silicon alloys attack the refractory materials in the induction furnace in which the metals are made. Also, the source of supply for calcium-silicon alloys is limited at times so that the alloys are not always readily available. Further, metallurgically the calcium-silicon alloy contains too high a silicon content, so to use sufficient alloy to supply enough calcium to reduce the rare earths results in a high silicon-rare earth alloy which is not always desirable. Substitution of a less expensive reducing agent for the calcium-silicide is a desirable objective. An area of improvement resides in improving the recovery of the rare earth metal from its oxide and obtaining a final alloy having a higher percentage of the rare earth metal. The presence of some calcium and a low percentage of silicon is also preferred for some customer applications.
As is well known, the metals columbium, titanium and zirconium are useful alloying metals for steel to impart desired properties ot it. Titanium is ordinarily added as ferrotitanium; however, it is a difficult alloy to make. Titanium is available at times in the form of scrap, but when it is not readily available the price rises and the industry reverts to the use of ferrotitanium. The above is also true in part for columbium and zirconium. One disadvantage of the prior art practice of using alloys of titanium and zirconium for addition to steel is that there is no procedure available for making the alloys directly from ore concentrates or raw materials.
Accordingly, it is a principal object of this invention to provide a method for producing rare earth metal alloys which avoids the use of calcium-silicon alloys, gives a high recovery of the rare earth metal from the oxide, provides a final alloy having a higher percentage of rare earth metal, contains a low silicon content, and some calcium and aluminum.
It is also an object of this invention to provide a method for making alloys of ferrocolumbium, ferrotitanium and ferrozirconium, alloys used in the past for alloying these latter two metals with steel.
It is a further object of this invention to provide a method for making alloys of columbium, titanium and zirconium for use in steel making directly from the ore concentrates of these metals.